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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-EXEC"
>31.3. Command Execution Functions</A
></H1
><P
>   Once a connection to a database server has been successfully
   established, the functions described here are used to perform
   SQL queries and commands.
  </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-EXEC-MAIN"
>31.3.1. Main Functions</A
></H2
><P
>    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQEXEC"
></A
><CODE
CLASS="FUNCTION"
>PQexec</CODE
>
       </DT
><DD
><P
>        Submits a command to the server and waits for the result.

</P><PRE
CLASS="SYNOPSIS"
>PGresult *PQexec(PGconn *conn, const char *command);</PRE
><P>
       </P
><P
>        Returns a <TT
CLASS="STRUCTNAME"
>PGresult</TT
> pointer or possibly a null
        pointer.  A non-null pointer will generally be returned except in
        out-of-memory conditions or serious errors such as inability to send
        the command to the server.  The <CODE
CLASS="FUNCTION"
>PQresultStatus</CODE
> function
        should be called to check the return value for any errors (including
        the value of a null pointer, in which case it will return
        <TT
CLASS="SYMBOL"
>PGRES_FATAL_ERROR</TT
>).  Use
        <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to get more information about such
        errors.
       </P
></DD
></DL
></DIV
><P>

    The command string can include multiple SQL commands
    (separated by semicolons).  Multiple queries sent in a single
    <CODE
CLASS="FUNCTION"
>PQexec</CODE
> call are processed in a single transaction, unless
    there are explicit <TT
CLASS="COMMAND"
>BEGIN</TT
>/<TT
CLASS="COMMAND"
>COMMIT</TT
>
    commands included in the query string to divide it into multiple
    transactions.  Note however that the returned
    <TT
CLASS="STRUCTNAME"
>PGresult</TT
> structure describes only the result
    of the last command executed from the string.  Should one of the
    commands fail, processing of the string stops with it and the returned
    <TT
CLASS="STRUCTNAME"
>PGresult</TT
> describes the error condition.
   </P
><P
>    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQEXECPARAMS"
></A
><CODE
CLASS="FUNCTION"
>PQexecParams</CODE
>
       </DT
><DD
><P
>        Submits a command to the server and waits for the result,
        with the ability to pass parameters separately from the SQL
        command text.

</P><PRE
CLASS="SYNOPSIS"
>PGresult *PQexecParams(PGconn *conn,
                       const char *command,
                       int nParams,
                       const Oid *paramTypes,
                       const char * const *paramValues,
                       const int *paramLengths,
                       const int *paramFormats,
                       int resultFormat);</PRE
><P>
       </P
><P
>        <CODE
CLASS="FUNCTION"
>PQexecParams</CODE
> is like <CODE
CLASS="FUNCTION"
>PQexec</CODE
>, but offers additional
        functionality: parameter values can be specified separately from the command
        string proper, and query results can be requested in either text or binary
        format.  <CODE
CLASS="FUNCTION"
>PQexecParams</CODE
> is supported only in protocol 3.0 and later
        connections; it will fail when using protocol 2.0.
       </P
><P
>        The function arguments are:

        <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="PARAMETER"
>conn</TT
></DT
><DD
><P
>            The connection object to send the command through.
           </P
></DD
><DT
><TT
CLASS="PARAMETER"
>command</TT
></DT
><DD
><P
>            The SQL command string to be executed. If parameters are used,
            they are referred to in the command string as <TT
CLASS="LITERAL"
>$1</TT
>,
            <TT
CLASS="LITERAL"
>$2</TT
>, etc.
           </P
></DD
><DT
><TT
CLASS="PARAMETER"
>nParams</TT
></DT
><DD
><P
>            The number of parameters supplied; it is the length of the arrays
            <TT
CLASS="PARAMETER"
>paramTypes[]</TT
>, <TT
CLASS="PARAMETER"
>paramValues[]</TT
>,
            <TT
CLASS="PARAMETER"
>paramLengths[]</TT
>, and <TT
CLASS="PARAMETER"
>paramFormats[]</TT
>. (The
            array pointers can be <TT
CLASS="SYMBOL"
>NULL</TT
> when <TT
CLASS="PARAMETER"
>nParams</TT
>
            is zero.)
           </P
></DD
><DT
><TT
CLASS="PARAMETER"
>paramTypes[]</TT
></DT
><DD
><P
>            Specifies, by OID, the data types to be assigned to the
            parameter symbols.  If <TT
CLASS="PARAMETER"
>paramTypes</TT
> is
            <TT
CLASS="SYMBOL"
>NULL</TT
>, or any particular element in the array
            is zero, the server infers a data type for the parameter symbol
            in the same way it would do for an untyped literal string.
           </P
></DD
><DT
><TT
CLASS="PARAMETER"
>paramValues[]</TT
></DT
><DD
><P
>            Specifies the actual values of the parameters.  A null pointer
            in this array means the corresponding parameter is null;
            otherwise the pointer points to a zero-terminated text string
            (for text format) or binary data in the format expected by the
            server (for binary format).
           </P
></DD
><DT
><TT
CLASS="PARAMETER"
>paramLengths[]</TT
></DT
><DD
><P
>            Specifies the actual data lengths of binary-format parameters.
            It is ignored for null parameters and text-format parameters.
            The array pointer can be null when there are no binary parameters.
           </P
></DD
><DT
><TT
CLASS="PARAMETER"
>paramFormats[]</TT
></DT
><DD
><P
>            Specifies whether parameters are text (put a zero in the
            array entry for the corresponding parameter) or binary (put
            a one in the array entry for the corresponding parameter).
            If the array pointer is null then all parameters are presumed
            to be text strings.
           </P
><P
>            Values passed in binary format require knowledge of
            the internal representation expected by the backend.
            For example, integers must be passed in network byte
            order.  Passing <TT
CLASS="TYPE"
>numeric</TT
> values requires
            knowledge of the server storage format, as implemented
            in
            <TT
CLASS="FILENAME"
>src/backend/utils/adt/numeric.c::numeric_send()</TT
> and
            <TT
CLASS="FILENAME"
>src/backend/utils/adt/numeric.c::numeric_recv()</TT
>.
           </P
></DD
><DT
><TT
CLASS="PARAMETER"
>resultFormat</TT
></DT
><DD
><P
>            Specify zero to obtain results in text format, or one to obtain
            results in binary format.  (There is not currently a provision
            to obtain different result columns in different formats,
            although that is possible in the underlying protocol.)
           </P
></DD
></DL
></DIV
><P>
       </P
></DD
></DL
></DIV
><P>
   </P
><P
>    The primary advantage of <CODE
CLASS="FUNCTION"
>PQexecParams</CODE
> over
    <CODE
CLASS="FUNCTION"
>PQexec</CODE
> is that parameter values can be separated from the
    command string, thus avoiding the need for tedious and error-prone
    quoting and escaping.
   </P
><P
>    Unlike <CODE
CLASS="FUNCTION"
>PQexec</CODE
>, <CODE
CLASS="FUNCTION"
>PQexecParams</CODE
> allows at most
    one SQL command in the given string.  (There can be semicolons in it,
    but not more than one nonempty command.)  This is a limitation of the
    underlying protocol, but has some usefulness as an extra defense against
    SQL-injection attacks.
   </P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>     Specifying parameter types via OIDs is tedious, particularly if you prefer
     not to hard-wire particular OID values into your program.  However, you can
     avoid doing so even in cases where the server by itself cannot determine the
     type of the parameter, or chooses a different type than you want.  In the
     SQL command text, attach an explicit cast to the parameter symbol to show what
     data type you will send.  For example:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM mytable WHERE x = $1::bigint;</PRE
><P>
     This forces parameter <TT
CLASS="LITERAL"
>$1</TT
> to be treated as <TT
CLASS="TYPE"
>bigint</TT
>, whereas
     by default it would be assigned the same type as <TT
CLASS="LITERAL"
>x</TT
>.  Forcing the
     parameter type decision, either this way or by specifying a numeric type OID,
     is strongly recommended when sending parameter values in binary format, because
     binary format has less redundancy than text format and so there is less chance
     that the server will detect a type mismatch mistake for you.
    </P
></BLOCKQUOTE
></DIV
><P
>    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQPREPARE"
></A
><CODE
CLASS="FUNCTION"
>PQprepare</CODE
>
       </DT
><DD
><P
>        Submits a request to create a prepared statement with the
        given parameters, and waits for completion.
</P><PRE
CLASS="SYNOPSIS"
>PGresult *PQprepare(PGconn *conn,
                    const char *stmtName,
                    const char *query,
                    int nParams,
                    const Oid *paramTypes);</PRE
><P>
       </P
><P
>        <CODE
CLASS="FUNCTION"
>PQprepare</CODE
> creates a prepared statement for later
        execution with <CODE
CLASS="FUNCTION"
>PQexecPrepared</CODE
>.  This feature allows
        commands that will be used repeatedly to be parsed and planned just
        once, rather than each time they are executed.
        <CODE
CLASS="FUNCTION"
>PQprepare</CODE
> is supported only in protocol 3.0 and later
        connections; it will fail when using protocol 2.0.
       </P
><P
>        The function creates a prepared statement named
        <TT
CLASS="PARAMETER"
>stmtName</TT
> from the <TT
CLASS="PARAMETER"
>query</TT
> string, which
        must contain a single SQL command.  <TT
CLASS="PARAMETER"
>stmtName</TT
> can be
        <TT
CLASS="LITERAL"
>""</TT
> to create an unnamed statement, in which case any
        pre-existing unnamed statement is automatically replaced; otherwise
        it is an error if the statement name is already defined in the
        current session.  If any parameters are used, they are referred
        to in the query as <TT
CLASS="LITERAL"
>$1</TT
>, <TT
CLASS="LITERAL"
>$2</TT
>, etc.
        <TT
CLASS="PARAMETER"
>nParams</TT
> is the number of parameters for which types
        are pre-specified in the array <TT
CLASS="PARAMETER"
>paramTypes[]</TT
>.  (The
        array pointer can be <TT
CLASS="SYMBOL"
>NULL</TT
> when
        <TT
CLASS="PARAMETER"
>nParams</TT
> is zero.) <TT
CLASS="PARAMETER"
>paramTypes[]</TT
>
        specifies, by OID, the data types to be assigned to the parameter
        symbols.  If <TT
CLASS="PARAMETER"
>paramTypes</TT
> is <TT
CLASS="SYMBOL"
>NULL</TT
>,
        or any particular element in the array is zero, the server assigns
        a data type to the parameter symbol in the same way it would do
        for an untyped literal string.  Also, the query can use parameter
        symbols with numbers higher than <TT
CLASS="PARAMETER"
>nParams</TT
>; data types
        will be inferred for these symbols as well.  (See
        <CODE
CLASS="FUNCTION"
>PQdescribePrepared</CODE
> for a means to find out
        what data types were inferred.)
       </P
><P
>        As with <CODE
CLASS="FUNCTION"
>PQexec</CODE
>, the result is normally a
        <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object whose contents indicate
        server-side success or failure.  A null result indicates
        out-of-memory or inability to send the command at all.  Use
        <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to get more information about
        such errors.
       </P
></DD
></DL
></DIV
><P>

    Prepared statements for use with <CODE
CLASS="FUNCTION"
>PQexecPrepared</CODE
> can also
    be created by executing SQL <A
HREF="sql-prepare.html"
>PREPARE</A
>
    statements.  Also, although there is no <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>
    function for deleting a prepared statement, the SQL <A
HREF="sql-deallocate.html"
>DEALLOCATE</A
> statement
    can be used for that purpose.
   </P
><P
>    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQEXECPREPARED"
></A
><CODE
CLASS="FUNCTION"
>PQexecPrepared</CODE
>
       </DT
><DD
><P
>        Sends a request to execute a prepared statement with given
        parameters, and waits for the result.
</P><PRE
CLASS="SYNOPSIS"
>PGresult *PQexecPrepared(PGconn *conn,
                         const char *stmtName,
                         int nParams,
                         const char * const *paramValues,
                         const int *paramLengths,
                         const int *paramFormats,
                         int resultFormat);</PRE
><P>
       </P
><P
>        <CODE
CLASS="FUNCTION"
>PQexecPrepared</CODE
> is like <CODE
CLASS="FUNCTION"
>PQexecParams</CODE
>,
        but the command to be executed is specified by naming a
        previously-prepared statement, instead of giving a query string.
        This feature allows commands that will be used repeatedly to be
        parsed and planned just once, rather than each time they are
        executed.  The statement must have been prepared previously in
        the current session.  <CODE
CLASS="FUNCTION"
>PQexecPrepared</CODE
> is supported
        only in protocol 3.0 and later connections; it will fail when
        using protocol 2.0.
       </P
><P
>        The parameters are identical to <CODE
CLASS="FUNCTION"
>PQexecParams</CODE
>, except that the
        name of a prepared statement is given instead of a query string, and the
        <TT
CLASS="PARAMETER"
>paramTypes[]</TT
> parameter is not present (it is not needed since
        the prepared statement's parameter types were determined when it was created).
       </P
></DD
><DT
><A
NAME="LIBPQ-PQDESCRIBEPREPARED"
></A
><CODE
CLASS="FUNCTION"
>PQdescribePrepared</CODE
>
       </DT
><DD
><P
>        Submits a request to obtain information about the specified
        prepared statement, and waits for completion.
</P><PRE
CLASS="SYNOPSIS"
>PGresult *PQdescribePrepared(PGconn *conn, const char *stmtName);</PRE
><P>
       </P
><P
>        <CODE
CLASS="FUNCTION"
>PQdescribePrepared</CODE
> allows an application to obtain
        information about a previously prepared statement.
        <CODE
CLASS="FUNCTION"
>PQdescribePrepared</CODE
> is supported only in protocol 3.0
        and later connections; it will fail when using protocol 2.0.
       </P
><P
>        <TT
CLASS="PARAMETER"
>stmtName</TT
> can be <TT
CLASS="LITERAL"
>""</TT
> or <TT
CLASS="SYMBOL"
>NULL</TT
> to reference
        the unnamed statement, otherwise it must be the name of an existing
        prepared statement.  On success, a <TT
CLASS="STRUCTNAME"
>PGresult</TT
> with
        status <TT
CLASS="LITERAL"
>PGRES_COMMAND_OK</TT
> is returned.  The
        functions <CODE
CLASS="FUNCTION"
>PQnparams</CODE
> and
        <CODE
CLASS="FUNCTION"
>PQparamtype</CODE
> can be applied to this
        <TT
CLASS="STRUCTNAME"
>PGresult</TT
> to obtain information about the parameters
        of the prepared statement, and the functions
        <CODE
CLASS="FUNCTION"
>PQnfields</CODE
>, <CODE
CLASS="FUNCTION"
>PQfname</CODE
>,
        <CODE
CLASS="FUNCTION"
>PQftype</CODE
>, etc provide information about the
        result columns (if any) of the statement.
       </P
></DD
><DT
><A
NAME="LIBPQ-PQDESCRIBEPORTAL"
></A
><CODE
CLASS="FUNCTION"
>PQdescribePortal</CODE
>
       </DT
><DD
><P
>        Submits a request to obtain information about the specified
        portal, and waits for completion.
</P><PRE
CLASS="SYNOPSIS"
>PGresult *PQdescribePortal(PGconn *conn, const char *portalName);</PRE
><P>
       </P
><P
>        <CODE
CLASS="FUNCTION"
>PQdescribePortal</CODE
> allows an application to obtain
        information about a previously created portal.
        (<SPAN
CLASS="APPLICATION"
>libpq</SPAN
> does not provide any direct access to
        portals, but you can use this function to inspect the properties
        of a cursor created with a <TT
CLASS="COMMAND"
>DECLARE CURSOR</TT
> SQL command.)
        <CODE
CLASS="FUNCTION"
>PQdescribePortal</CODE
> is supported only in protocol 3.0
        and later connections; it will fail when using protocol 2.0.
       </P
><P
>        <TT
CLASS="PARAMETER"
>portalName</TT
> can be <TT
CLASS="LITERAL"
>""</TT
> or <TT
CLASS="SYMBOL"
>NULL</TT
> to reference
        the unnamed portal, otherwise it must be the name of an existing
        portal.  On success, a <TT
CLASS="STRUCTNAME"
>PGresult</TT
> with status
        <TT
CLASS="LITERAL"
>PGRES_COMMAND_OK</TT
> is returned.  The functions
        <CODE
CLASS="FUNCTION"
>PQnfields</CODE
>, <CODE
CLASS="FUNCTION"
>PQfname</CODE
>,
        <CODE
CLASS="FUNCTION"
>PQftype</CODE
>, etc can be applied to the
        <TT
CLASS="STRUCTNAME"
>PGresult</TT
> to obtain information about the result
        columns (if any) of the portal.
       </P
></DD
></DL
></DIV
><P>
   </P
><P
>    The <TT
CLASS="STRUCTNAME"
>PGresult</TT
>
    structure encapsulates the result returned by the server.
    <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> application programmers should be
    careful to maintain the <TT
CLASS="STRUCTNAME"
>PGresult</TT
> abstraction.
    Use the accessor functions below to get at the contents of
    <TT
CLASS="STRUCTNAME"
>PGresult</TT
>.  Avoid directly referencing the
    fields of the <TT
CLASS="STRUCTNAME"
>PGresult</TT
> structure because they
    are subject to change in the future.

    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQRESULTSTATUS"
></A
><CODE
CLASS="FUNCTION"
>PQresultStatus</CODE
>
       </DT
><DD
><P
>        Returns the result status of the command.
</P><PRE
CLASS="SYNOPSIS"
>ExecStatusType PQresultStatus(const PGresult *res);</PRE
><P>
       </P
><P
>        <CODE
CLASS="FUNCTION"
>PQresultStatus</CODE
> can return one of the following values:

        <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PGRES-EMPTY-QUERY"
></A
><TT
CLASS="LITERAL"
>PGRES_EMPTY_QUERY</TT
></DT
><DD
><P
>            The string sent to the server was empty.
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-COMMAND-OK"
></A
><TT
CLASS="LITERAL"
>PGRES_COMMAND_OK</TT
></DT
><DD
><P
>            Successful completion of a command returning no data.
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-TUPLES-OK"
></A
><TT
CLASS="LITERAL"
>PGRES_TUPLES_OK</TT
></DT
><DD
><P
>            Successful completion of a command returning data (such as
            a <TT
CLASS="COMMAND"
>SELECT</TT
> or <TT
CLASS="COMMAND"
>SHOW</TT
>).
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-COPY-OUT"
></A
><TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
></DT
><DD
><P
>            Copy Out (from server) data transfer started.
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-COPY-IN"
></A
><TT
CLASS="LITERAL"
>PGRES_COPY_IN</TT
></DT
><DD
><P
>            Copy In (to server) data transfer started.
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-BAD-RESPONSE"
></A
><TT
CLASS="LITERAL"
>PGRES_BAD_RESPONSE</TT
></DT
><DD
><P
>            The server's response was not understood.
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-NONFATAL-ERROR"
></A
><TT
CLASS="LITERAL"
>PGRES_NONFATAL_ERROR</TT
></DT
><DD
><P
>            A nonfatal error (a notice or warning) occurred.
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-FATAL-ERROR"
></A
><TT
CLASS="LITERAL"
>PGRES_FATAL_ERROR</TT
></DT
><DD
><P
>            A fatal error occurred.
           </P
></DD
><DT
><A
NAME="LIBPQ-PGRES-COPY-BOTH"
></A
><TT
CLASS="LITERAL"
>PGRES_COPY_BOTH</TT
></DT
><DD
><P
>            Copy In/Out (to and from server) data transfer started.  This is
            currently used only for streaming replication.
           </P
></DD
></DL
></DIV
><P>

        If the result status is <TT
CLASS="LITERAL"
>PGRES_TUPLES_OK</TT
>, then
        the functions described below can be used to retrieve the rows
        returned by the query.  Note that a <TT
CLASS="COMMAND"
>SELECT</TT
>
        command that happens to retrieve zero rows still shows
        <TT
CLASS="LITERAL"
>PGRES_TUPLES_OK</TT
>.
        <TT
CLASS="LITERAL"
>PGRES_COMMAND_OK</TT
> is for commands that can never
        return rows (<TT
CLASS="COMMAND"
>INSERT</TT
>, <TT
CLASS="COMMAND"
>UPDATE</TT
>,
        etc.). A response of <TT
CLASS="LITERAL"
>PGRES_EMPTY_QUERY</TT
> might
        indicate a bug in the client software.
       </P
><P
>        A result of status <TT
CLASS="SYMBOL"
>PGRES_NONFATAL_ERROR</TT
> will
        never be returned directly by <CODE
CLASS="FUNCTION"
>PQexec</CODE
> or other
        query execution functions; results of this kind are instead passed
        to the notice processor (see <A
HREF="libpq-notice-processing.html"
>Section 31.11</A
>).
       </P
></DD
><DT
><A
NAME="LIBPQ-PQRESSTATUS"
></A
><CODE
CLASS="FUNCTION"
>PQresStatus</CODE
>
       </DT
><DD
><P
>        Converts the enumerated type returned by
        <CODE
CLASS="FUNCTION"
>PQresultStatus</CODE
> into a string constant describing the
        status code. The caller should not free the result.

</P><PRE
CLASS="SYNOPSIS"
>char *PQresStatus(ExecStatusType status);</PRE
><P>
       </P
></DD
><DT
><A
NAME="LIBPQ-PQRESULTERRORMESSAGE"
></A
><CODE
CLASS="FUNCTION"
>PQresultErrorMessage</CODE
>
       </DT
><DD
><P
>        Returns the error message associated with the command, or an empty string
        if there was no error.
</P><PRE
CLASS="SYNOPSIS"
>char *PQresultErrorMessage(const PGresult *res);</PRE
><P>
        If there was an error, the returned string will include a trailing
        newline.  The caller should not free the result directly. It will
        be freed when the associated <TT
CLASS="STRUCTNAME"
>PGresult</TT
> handle is
        passed to <CODE
CLASS="FUNCTION"
>PQclear</CODE
>.
       </P
><P
>        Immediately following a <CODE
CLASS="FUNCTION"
>PQexec</CODE
> or
        <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> call,
        <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> (on the connection) will return
        the same string as <CODE
CLASS="FUNCTION"
>PQresultErrorMessage</CODE
> (on
        the result).  However, a <TT
CLASS="STRUCTNAME"
>PGresult</TT
> will
        retain its error message until destroyed, whereas the connection's
        error message will change when subsequent operations are done.
        Use <CODE
CLASS="FUNCTION"
>PQresultErrorMessage</CODE
> when you want to
        know the status associated with a particular
        <TT
CLASS="STRUCTNAME"
>PGresult</TT
>; use
        <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> when you want to know the
        status from the latest operation on the connection.
       </P
></DD
><DT
><A
NAME="LIBPQ-PQRESULTERRORFIELD"
></A
><CODE
CLASS="FUNCTION"
>PQresultErrorField</CODE
></DT
><DD
><P
>        Returns an individual field of an error report.
</P><PRE
CLASS="SYNOPSIS"
>char *PQresultErrorField(const PGresult *res, int fieldcode);</PRE
><P>
        <TT
CLASS="PARAMETER"
>fieldcode</TT
> is an error field identifier; see the symbols
        listed below.  <TT
CLASS="SYMBOL"
>NULL</TT
> is returned if the
        <TT
CLASS="STRUCTNAME"
>PGresult</TT
> is not an error or warning result,
        or does not include the specified field.  Field values will normally
        not include a trailing newline. The caller should not free the
        result directly. It will be freed when the
        associated <TT
CLASS="STRUCTNAME"
>PGresult</TT
> handle is passed to
        <CODE
CLASS="FUNCTION"
>PQclear</CODE
>.
       </P
><P
>        The following field codes are available:
        <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PG-DIAG-SEVERITY"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_SEVERITY</TT
></DT
><DD
><P
>            The severity; the field contents are <TT
CLASS="LITERAL"
>ERROR</TT
>,
            <TT
CLASS="LITERAL"
>FATAL</TT
>, or <TT
CLASS="LITERAL"
>PANIC</TT
> (in an error message),
            or <TT
CLASS="LITERAL"
>WARNING</TT
>, <TT
CLASS="LITERAL"
>NOTICE</TT
>, <TT
CLASS="LITERAL"
>DEBUG</TT
>,
            <TT
CLASS="LITERAL"
>INFO</TT
>, or <TT
CLASS="LITERAL"
>LOG</TT
> (in a notice message), or
            a localized translation of one of these.  Always present.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-SQLSTATE"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_SQLSTATE</TT
></DT
><DD
><P
>            The SQLSTATE code for the error. The SQLSTATE code identifies
            the type of error that has occurred; it can be used by
            front-end applications to perform specific operations (such
            as error handling) in response to a particular database error.
            For a list of the possible SQLSTATE codes, see <A
HREF="errcodes-appendix.html"
>Appendix A</A
>. This field is not localizable,
            and is always present.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-MESSAGE-PRIMARY"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_MESSAGE_PRIMARY</TT
></DT
><DD
><P
>            The primary human-readable error message (typically one line).
            Always present.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-MESSAGE-DETAIL"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_MESSAGE_DETAIL</TT
></DT
><DD
><P
>            Detail: an optional secondary error message carrying more
            detail about the problem.  Might run to multiple lines.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-MESSAGE-HINT"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_MESSAGE_HINT</TT
></DT
><DD
><P
>            Hint: an optional suggestion what to do about the problem.
            This is intended to differ from detail in that it offers advice
            (potentially inappropriate) rather than hard facts.  Might
            run to multiple lines.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-STATEMENT-POSITION"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_STATEMENT_POSITION</TT
></DT
><DD
><P
>            A string containing a decimal integer indicating an error cursor
            position as an index into the original statement string.  The
            first character has index 1, and positions are measured in
            characters not bytes.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-INTERNAL-POSITION"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_INTERNAL_POSITION</TT
></DT
><DD
><P
>            This is defined the same as the
            <TT
CLASS="SYMBOL"
>PG_DIAG_STATEMENT_POSITION</TT
> field, but it is used
            when the cursor position refers to an internally generated
            command rather than the one submitted by the client.  The
            <TT
CLASS="SYMBOL"
>PG_DIAG_INTERNAL_QUERY</TT
> field will always appear when
            this field appears.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-INTERNAL-QUERY"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_INTERNAL_QUERY</TT
></DT
><DD
><P
>            The text of a failed internally-generated command.  This could
            be, for example, a SQL query issued by a PL/pgSQL function.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-CONTEXT"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_CONTEXT</TT
></DT
><DD
><P
>            An indication of the context in which the error occurred.
            Presently this includes a call stack traceback of active
            procedural language functions and internally-generated queries.
            The trace is one entry per line, most recent first.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-SOURCE-FILE"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_SOURCE_FILE</TT
></DT
><DD
><P
>            The file name of the source-code location where the error was
            reported.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-SOURCE-LINE"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_SOURCE_LINE</TT
></DT
><DD
><P
>            The line number of the source-code location where the error
            was reported.
           </P
></DD
><DT
><A
NAME="LIBPQ-PG-DIAG-SOURCE-FUNCTION"
></A
><TT
CLASS="SYMBOL"
>PG_DIAG_SOURCE_FUNCTION</TT
></DT
><DD
><P
>            The name of the source-code function reporting the error.
           </P
></DD
></DL
></DIV
><P>
       </P
><P
>        The client is responsible for formatting displayed information to meet
        its needs; in particular it should break long lines as needed.
        Newline characters appearing in the error message fields should be
        treated as paragraph breaks, not line breaks.
       </P
><P
>        Errors generated internally by <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will
        have severity and primary message, but typically no other fields.
        Errors returned by a pre-3.0-protocol server will include severity and
        primary message, and sometimes a detail message, but no other fields.
       </P
><P
>        Note that error fields are only available from
        <TT
CLASS="STRUCTNAME"
>PGresult</TT
> objects, not
        <TT
CLASS="STRUCTNAME"
>PGconn</TT
> objects; there is no
        <CODE
CLASS="FUNCTION"
>PQerrorField</CODE
> function.
       </P
></DD
><DT
><A
NAME="LIBPQ-PQCLEAR"
></A
><CODE
CLASS="FUNCTION"
>PQclear</CODE
></DT
><DD
><P
>        Frees  the  storage  associated with a
        <TT
CLASS="STRUCTNAME"
>PGresult</TT
>.  Every command result should be
        freed via <CODE
CLASS="FUNCTION"
>PQclear</CODE
> when it  is  no  longer
        needed.

</P><PRE
CLASS="SYNOPSIS"
>void PQclear(PGresult *res);</PRE
><P>
       </P
><P
>        You can keep a <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object around for
        as long as you need it; it does not go away when you issue a new
        command, nor even if you close the connection.  To get rid of it,
        you must call <CODE
CLASS="FUNCTION"
>PQclear</CODE
>.  Failure to do this
        will result in memory leaks in your application.
       </P
></DD
></DL
></DIV
><P>
   </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-EXEC-SELECT-INFO"
>31.3.2. Retrieving Query Result Information</A
></H2
><P
>    These functions are used to extract information from a
    <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object that represents a successful
    query result (that is, one that has status
    <TT
CLASS="LITERAL"
>PGRES_TUPLES_OK</TT
>).  They can also be used to extract
    information from a successful Describe operation: a Describe's result
    has all the same column information that actual execution of the query
    would provide, but it has zero rows.  For objects with other status values,
    these functions will act as though the result has zero rows and zero columns.
   </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQNTUPLES"
></A
><CODE
CLASS="FUNCTION"
>PQntuples</CODE
>
      </DT
><DD
><P
>       Returns the number of rows (tuples) in the query result.  Because
       it returns an integer result, large result sets might overflow the
       return value on 32-bit operating systems.

</P><PRE
CLASS="SYNOPSIS"
>int PQntuples(const PGresult *res);</PRE
><P>

      </P
></DD
><DT
><A
NAME="LIBPQ-PQNFIELDS"
></A
><CODE
CLASS="FUNCTION"
>PQnfields</CODE
>
      </DT
><DD
><P
>       Returns the number of columns (fields) in each row of the query
       result.

</P><PRE
CLASS="SYNOPSIS"
>int PQnfields(const PGresult *res);</PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFNAME"
></A
><CODE
CLASS="FUNCTION"
>PQfname</CODE
>
      </DT
><DD
><P
>       Returns the column name associated with the given column number.
       Column numbers start at 0. The caller should not free the result
       directly. It will be freed when the associated
       <TT
CLASS="STRUCTNAME"
>PGresult</TT
> handle is passed to
       <CODE
CLASS="FUNCTION"
>PQclear</CODE
>.
</P><PRE
CLASS="SYNOPSIS"
>char *PQfname(const PGresult *res,
              int column_number);</PRE
><P>
      </P
><P
>       <TT
CLASS="SYMBOL"
>NULL</TT
> is returned if the column number is out of range.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFNUMBER"
></A
><CODE
CLASS="FUNCTION"
>PQfnumber</CODE
>
      </DT
><DD
><P
>       Returns the column number associated with the given column name.
</P><PRE
CLASS="SYNOPSIS"
>int PQfnumber(const PGresult *res,
              const char *column_name);</PRE
><P>
      </P
><P
>       -1 is returned if the given name does not match any column.
      </P
><P
>       The given name is treated like an identifier in an SQL command,
       that is, it is downcased unless double-quoted.  For example, given
       a query result generated from the SQL command:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 1 AS FOO, 2 AS "BAR";</PRE
><P>
       we would have the results:
</P><PRE
CLASS="PROGRAMLISTING"
>PQfname(res, 0)              <I
CLASS="LINEANNOTATION"
>foo</I
>
PQfname(res, 1)              <I
CLASS="LINEANNOTATION"
>BAR</I
>
PQfnumber(res, "FOO")        <I
CLASS="LINEANNOTATION"
>0</I
>
PQfnumber(res, "foo")        <I
CLASS="LINEANNOTATION"
>0</I
>
PQfnumber(res, "BAR")        <I
CLASS="LINEANNOTATION"
>-1</I
>
PQfnumber(res, "\"BAR\"")    <I
CLASS="LINEANNOTATION"
>1</I
></PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFTABLE"
></A
><CODE
CLASS="FUNCTION"
>PQftable</CODE
>
      </DT
><DD
><P
>       Returns the OID of the table from which the given column was
       fetched.  Column numbers start at 0.
</P><PRE
CLASS="SYNOPSIS"
>Oid PQftable(const PGresult *res,
             int column_number);</PRE
><P>
      </P
><P
>       <TT
CLASS="LITERAL"
>InvalidOid</TT
> is returned if the column number is out of range,
       or if the specified column is not a simple reference to a table column,
       or when using pre-3.0 protocol.
       You can query the system table <TT
CLASS="LITERAL"
>pg_class</TT
> to determine
       exactly which table is referenced.
      </P
><P
>       The type <TT
CLASS="TYPE"
>Oid</TT
> and the constant
       <TT
CLASS="LITERAL"
>InvalidOid</TT
> will be defined when you include
       the <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> header file. They will both
       be some integer type.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFTABLECOL"
></A
><CODE
CLASS="FUNCTION"
>PQftablecol</CODE
>
      </DT
><DD
><P
>       Returns the column number (within its table) of the column making
       up the specified query result column.  Query-result column numbers
       start at 0, but table columns have nonzero numbers.
</P><PRE
CLASS="SYNOPSIS"
>int PQftablecol(const PGresult *res,
                int column_number);</PRE
><P>
      </P
><P
>       Zero is returned if the column number is out of range, or if the
       specified column is not a simple reference to a table column, or
       when using pre-3.0 protocol.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFFORMAT"
></A
><CODE
CLASS="FUNCTION"
>PQfformat</CODE
>
      </DT
><DD
><P
>       Returns the format code indicating the format of the given
       column.  Column numbers start at 0.
</P><PRE
CLASS="SYNOPSIS"
>int PQfformat(const PGresult *res,
              int column_number);</PRE
><P>
      </P
><P
>       Format code zero indicates textual data representation, while format
       code one indicates binary representation.  (Other codes are reserved
       for future definition.)
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFTYPE"
></A
><CODE
CLASS="FUNCTION"
>PQftype</CODE
>
      </DT
><DD
><P
>       Returns the data type associated with the given  column number.
       The  integer  returned is the internal OID number of the type.
       Column numbers start at 0.
</P><PRE
CLASS="SYNOPSIS"
>Oid PQftype(const PGresult *res,
            int column_number);</PRE
><P>
      </P
><P
>       You can query the system table <TT
CLASS="LITERAL"
>pg_type</TT
> to
       obtain the names and properties of the various data types. The
       <ACRONYM
CLASS="ACRONYM"
>OID</ACRONYM
>s of the built-in data types are defined
       in the file <TT
CLASS="FILENAME"
>src/include/catalog/pg_type.h</TT
>
       in the source tree.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFMOD"
></A
><CODE
CLASS="FUNCTION"
>PQfmod</CODE
>
      </DT
><DD
><P
>       Returns  the type modifier of the column associated with the
       given column number.  Column numbers start at 0.
</P><PRE
CLASS="SYNOPSIS"
>int PQfmod(const PGresult *res,
           int column_number);</PRE
><P>
      </P
><P
>       The interpretation of modifier values is type-specific; they
       typically indicate precision or size limits.  The value -1 is
       used to indicate <SPAN
CLASS="QUOTE"
>"no information available"</SPAN
>.  Most data
       types do not use modifiers, in which case the value is always
       -1.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFSIZE"
></A
><CODE
CLASS="FUNCTION"
>PQfsize</CODE
>
      </DT
><DD
><P
>       Returns  the  size  in bytes of the column associated with the
       given column number.  Column numbers start at 0.
</P><PRE
CLASS="SYNOPSIS"
>int PQfsize(const PGresult *res,
            int column_number);</PRE
><P>
      </P
><P
>       <CODE
CLASS="FUNCTION"
>PQfsize</CODE
> returns the space allocated for this column
       in a database row, in other words the size of the server's
       internal representation of the data type.  (Accordingly, it is
       not really very useful to clients.) A negative value indicates
       the data type is variable-length.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQBINARYTUPLES"
></A
><CODE
CLASS="FUNCTION"
>PQbinaryTuples</CODE
>
      </DT
><DD
><P
>       Returns 1 if the <TT
CLASS="STRUCTNAME"
>PGresult</TT
> contains binary data
       and 0 if it contains text data.
</P><PRE
CLASS="SYNOPSIS"
>int PQbinaryTuples(const PGresult *res);</PRE
><P>
      </P
><P
>       This function is deprecated (except for its use in connection with
       <TT
CLASS="COMMAND"
>COPY</TT
>), because it is possible for a single
       <TT
CLASS="STRUCTNAME"
>PGresult</TT
> to contain text data in some columns and
       binary data in others.  <CODE
CLASS="FUNCTION"
>PQfformat</CODE
> is preferred.
       <CODE
CLASS="FUNCTION"
>PQbinaryTuples</CODE
> returns 1 only if all columns of the
       result are binary (format 1).
      </P
></DD
><DT
><A
NAME="LIBPQ-PQGETVALUE"
></A
><CODE
CLASS="FUNCTION"
>PQgetvalue</CODE
>
       </DT
><DD
><P
>       Returns a single field value of one row of a
       <TT
CLASS="STRUCTNAME"
>PGresult</TT
>.  Row and column numbers start
       at 0.  The caller should not free the result directly.  It will
       be freed when the associated <TT
CLASS="STRUCTNAME"
>PGresult</TT
> handle is
       passed to <CODE
CLASS="FUNCTION"
>PQclear</CODE
>.
</P><PRE
CLASS="SYNOPSIS"
>char *PQgetvalue(const PGresult *res,
                 int row_number,
                 int column_number);</PRE
><P>
      </P
><P
>       For data in text format, the value returned by
       <CODE
CLASS="FUNCTION"
>PQgetvalue</CODE
> is a null-terminated character
       string  representation of the field value.  For data in binary
       format, the value is in the binary representation determined by
       the data type's <CODE
CLASS="FUNCTION"
>typsend</CODE
> and <CODE
CLASS="FUNCTION"
>typreceive</CODE
>
       functions.  (The value is actually followed by a zero byte in
       this case too, but that is not ordinarily useful, since the
       value is likely to contain embedded nulls.)
      </P
><P
>       An empty string is returned if the field value is null.  See
       <CODE
CLASS="FUNCTION"
>PQgetisnull</CODE
> to distinguish null values from
       empty-string values.
      </P
><P
>       The pointer returned  by  <CODE
CLASS="FUNCTION"
>PQgetvalue</CODE
> points
       to storage that is part of the <TT
CLASS="STRUCTNAME"
>PGresult</TT
>
       structure.  One should not modify the data it points to, and one
       must explicitly copy the data into other storage if it is to be
       used past the lifetime of the  <TT
CLASS="STRUCTNAME"
>PGresult</TT
>
       structure itself.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQGETISNULL"
></A
><CODE
CLASS="FUNCTION"
>PQgetisnull</CODE
>
      
      </DT
><DD
><P
>       Tests a field for a null value.  Row and column numbers start
       at 0.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetisnull(const PGresult *res,
                int row_number,
                int column_number);</PRE
><P>
      </P
><P
>       This function returns  1 if the field is null and 0 if it
       contains a non-null value.  (Note that
       <CODE
CLASS="FUNCTION"
>PQgetvalue</CODE
> will return an empty string,
       not a null pointer, for a null field.)
      </P
></DD
><DT
><A
NAME="LIBPQ-PQGETLENGTH"
></A
><CODE
CLASS="FUNCTION"
>PQgetlength</CODE
>
     </DT
><DD
><P
>       Returns the actual length of a field value in bytes.  Row and
       column numbers start at 0.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetlength(const PGresult *res,
                int row_number,
                int column_number);</PRE
><P>
      </P
><P
>       This is the actual data length for the particular data value,
       that is, the size of the object pointed to by
       <CODE
CLASS="FUNCTION"
>PQgetvalue</CODE
>.  For text data format this is
       the same as <CODE
CLASS="FUNCTION"
>strlen()</CODE
>.  For binary format this is
       essential information.  Note that one should <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
>
       rely on <CODE
CLASS="FUNCTION"
>PQfsize</CODE
> to obtain the actual data
       length.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQNPARAMS"
></A
><CODE
CLASS="FUNCTION"
>PQnparams</CODE
>
      </DT
><DD
><P
>       Returns the number of parameters of a prepared statement.
</P><PRE
CLASS="SYNOPSIS"
>int PQnparams(const PGresult *res);</PRE
><P>
      </P
><P
>       This function is only useful when inspecting the result of
       <CODE
CLASS="FUNCTION"
>PQdescribePrepared</CODE
>.  For other types of queries it
       will return zero.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQPARAMTYPE"
></A
><CODE
CLASS="FUNCTION"
>PQparamtype</CODE
>
      </DT
><DD
><P
>       Returns the data type of the indicated statement parameter.
       Parameter numbers start at 0.
</P><PRE
CLASS="SYNOPSIS"
>Oid PQparamtype(const PGresult *res, int param_number);</PRE
><P>
      </P
><P
>       This function is only useful when inspecting the result of
       <CODE
CLASS="FUNCTION"
>PQdescribePrepared</CODE
>.  For other types of queries it
       will return zero.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQPRINT"
></A
><CODE
CLASS="FUNCTION"
>PQprint</CODE
>
      </DT
><DD
><P
>       Prints out all the rows and,  optionally,  the column names  to
       the specified output stream.
</P><PRE
CLASS="SYNOPSIS"
>void PQprint(FILE *fout,      /* output stream */
             const PGresult *res,
             const PQprintOpt *po);
typedef struct
{
    pqbool  header;      /* print output field headings and row count */
    pqbool  align;       /* fill align the fields */
    pqbool  standard;    /* old brain dead format */
    pqbool  html3;       /* output HTML tables */
    pqbool  expanded;    /* expand tables */
    pqbool  pager;       /* use pager for output if needed */
    char    *fieldSep;   /* field separator */
    char    *tableOpt;   /* attributes for HTML table element */
    char    *caption;    /* HTML table caption */
    char    **fieldName; /* null-terminated array of replacement field names */
} PQprintOpt;</PRE
><P>
      </P
><P
>       This function was formerly used by <SPAN
CLASS="APPLICATION"
>psql</SPAN
>
       to print query results, but this is no longer the case.  Note
       that it assumes all the data is in text format.
      </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-EXEC-NONSELECT"
>31.3.3. Retrieving Other Result Information</A
></H2
><P
>    These functions are used to extract other information from
    <TT
CLASS="STRUCTNAME"
>PGresult</TT
> objects.
   </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQCMDSTATUS"
></A
><CODE
CLASS="FUNCTION"
>PQcmdStatus</CODE
>
      </DT
><DD
><P
>       Returns the command status tag from the SQL command that generated
       the <TT
CLASS="STRUCTNAME"
>PGresult</TT
>.
</P><PRE
CLASS="SYNOPSIS"
>char *PQcmdStatus(PGresult *res);</PRE
><P>
      </P
><P
>       Commonly this is just the name of the command, but it might include
       additional data such as the number of rows processed. The caller
       should not free the result directly. It will be freed when the
       associated <TT
CLASS="STRUCTNAME"
>PGresult</TT
> handle is passed to
       <CODE
CLASS="FUNCTION"
>PQclear</CODE
>.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQCMDTUPLES"
></A
><CODE
CLASS="FUNCTION"
>PQcmdTuples</CODE
>
      </DT
><DD
><P
>       Returns the number of rows affected by the SQL command.
</P><PRE
CLASS="SYNOPSIS"
>char *PQcmdTuples(PGresult *res);</PRE
><P>
      </P
><P
>       This function returns a string containing the number of rows
       affected by the <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> statement that generated the
       <TT
CLASS="STRUCTNAME"
>PGresult</TT
>. This function can only be used following
       the execution of a <TT
CLASS="COMMAND"
>SELECT</TT
>, <TT
CLASS="COMMAND"
>CREATE TABLE AS</TT
>,
       <TT
CLASS="COMMAND"
>INSERT</TT
>, <TT
CLASS="COMMAND"
>UPDATE</TT
>, <TT
CLASS="COMMAND"
>DELETE</TT
>,
       <TT
CLASS="COMMAND"
>MOVE</TT
>, <TT
CLASS="COMMAND"
>FETCH</TT
>, or <TT
CLASS="COMMAND"
>COPY</TT
> statement,
       or an <TT
CLASS="COMMAND"
>EXECUTE</TT
> of a prepared query that contains an
       <TT
CLASS="COMMAND"
>INSERT</TT
>, <TT
CLASS="COMMAND"
>UPDATE</TT
>, or <TT
CLASS="COMMAND"
>DELETE</TT
> statement.
       If the command that generated the <TT
CLASS="STRUCTNAME"
>PGresult</TT
> was anything
       else, <CODE
CLASS="FUNCTION"
>PQcmdTuples</CODE
> returns an empty string. The caller
       should not free the return value directly. It will be freed when
       the associated <TT
CLASS="STRUCTNAME"
>PGresult</TT
> handle is passed to
       <CODE
CLASS="FUNCTION"
>PQclear</CODE
>.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQOIDVALUE"
></A
><CODE
CLASS="FUNCTION"
>PQoidValue</CODE
>
      </DT
><DD
><P
>       Returns the OID
       of the inserted row, if the <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> command was an
       <TT
CLASS="COMMAND"
>INSERT</TT
> that inserted exactly one row into a table that
       has OIDs, or a <TT
CLASS="COMMAND"
>EXECUTE</TT
> of a prepared query containing
       a suitable <TT
CLASS="COMMAND"
>INSERT</TT
> statement.  Otherwise, this function
       returns <TT
CLASS="LITERAL"
>InvalidOid</TT
>. This function will also
       return <TT
CLASS="LITERAL"
>InvalidOid</TT
> if the table affected by the
       <TT
CLASS="COMMAND"
>INSERT</TT
> statement does not contain OIDs.
</P><PRE
CLASS="SYNOPSIS"
>Oid PQoidValue(const PGresult *res);</PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQOIDSTATUS"
></A
><CODE
CLASS="FUNCTION"
>PQoidStatus</CODE
>
      </DT
><DD
><P
>       This function is deprecated in favor of
       <CODE
CLASS="FUNCTION"
>PQoidValue</CODE
> and is not thread-safe.
       It returns a string with the OID of the inserted row, while
       <CODE
CLASS="FUNCTION"
>PQoidValue</CODE
> returns the OID value.
</P><PRE
CLASS="SYNOPSIS"
>char *PQoidStatus(const PGresult *res);</PRE
><P>
      </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-EXEC-ESCAPE-STRING"
>31.3.4. Escaping Strings for Inclusion in SQL Commands</A
></H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQESCAPELITERAL"
></A
><CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
>
      </DT
><DD
><P
></P><PRE
CLASS="SYNOPSIS"
>char *PQescapeLiteral(PGconn *conn, const char *str, size_t length);</PRE
><P>
     </P
><P
>      <CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
> escapes a string for
      use within an SQL command.  This is useful when inserting data
      values as literal constants in SQL commands.  Certain characters
      (such as quotes and backslashes) must be escaped to prevent them
      from being interpreted specially by the SQL parser.
      <CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
> performs this operation.
     </P
><P
>      <CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
> returns an escaped version of the
      <TT
CLASS="PARAMETER"
>str</TT
> parameter in memory allocated with
      <CODE
CLASS="FUNCTION"
>malloc()</CODE
>.  This memory should be freed using
      <CODE
CLASS="FUNCTION"
>PQfreemem()</CODE
> when the result is no longer needed.
      A terminating zero byte is not required, and should not be
      counted in <TT
CLASS="PARAMETER"
>length</TT
>.  (If a terminating zero byte is found
      before <TT
CLASS="PARAMETER"
>length</TT
> bytes are processed,
      <CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
> stops at the zero; the behavior is
      thus rather like <CODE
CLASS="FUNCTION"
>strncpy</CODE
>.) The
      return string has all special characters replaced so that they can
      be properly processed by the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
      string literal parser.  A terminating zero byte is also added.  The
      single quotes that must surround <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
      string literals are included in the result string.
     </P
><P
>      On error, <CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
> returns <TT
CLASS="SYMBOL"
>NULL</TT
> and a suitable
      message is stored in the <TT
CLASS="PARAMETER"
>conn</TT
> object.
     </P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>       It is especially important to do proper escaping when handling
       strings that were received from an untrustworthy source.
       Otherwise there is a security risk: you are vulnerable to
       <SPAN
CLASS="QUOTE"
>"SQL injection"</SPAN
> attacks wherein unwanted SQL commands are
       fed to your database.
      </P
></BLOCKQUOTE
></DIV
><P
>      Note that it is not necessary nor correct to do escaping when a data
      value is passed as a separate parameter in <CODE
CLASS="FUNCTION"
>PQexecParams</CODE
> or
      its sibling routines.
     </P
></DD
><DT
><A
NAME="LIBPQ-PQESCAPEIDENTIFIER"
></A
><CODE
CLASS="FUNCTION"
>PQescapeIdentifier</CODE
>
      </DT
><DD
><P
></P><PRE
CLASS="SYNOPSIS"
>char *PQescapeIdentifier(PGconn *conn, const char *str, size_t length);</PRE
><P>
     </P
><P
>      <CODE
CLASS="FUNCTION"
>PQescapeIdentifier</CODE
> escapes a string for
      use as an SQL identifier, such as a table, column, or function name.
      This is useful when a user-supplied identifier might contain
      special characters that would otherwise not be interpreted as part
      of the identifier by the SQL parser, or when the identifier might
      contain upper case characters whose case should be preserved.
     </P
><P
>      <CODE
CLASS="FUNCTION"
>PQescapeIdentifier</CODE
> returns a version of the
      <TT
CLASS="PARAMETER"
>str</TT
> parameter escaped as an SQL identifier
      in memory allocated with <CODE
CLASS="FUNCTION"
>malloc()</CODE
>.  This memory must be
      freed using <CODE
CLASS="FUNCTION"
>PQfreemem()</CODE
> when the result is no longer
      needed.  A terminating zero byte is not required, and should not be
      counted in <TT
CLASS="PARAMETER"
>length</TT
>.  (If a terminating zero byte is found
      before <TT
CLASS="PARAMETER"
>length</TT
> bytes are processed,
      <CODE
CLASS="FUNCTION"
>PQescapeIdentifier</CODE
> stops at the zero; the behavior is
      thus rather like <CODE
CLASS="FUNCTION"
>strncpy</CODE
>.) The
      return string has all special characters replaced so that it
      will be properly processed as an SQL identifier.  A terminating zero byte
      is also added.  The return string will also be surrounded by double
      quotes.
     </P
><P
>      On error, <CODE
CLASS="FUNCTION"
>PQescapeIdentifier</CODE
> returns <TT
CLASS="SYMBOL"
>NULL</TT
> and a suitable
      message is stored in the <TT
CLASS="PARAMETER"
>conn</TT
> object.
     </P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>       As with string literals, to prevent SQL injection attacks,
       SQL identifiers must be escaped when they are received from an
       untrustworthy source.
      </P
></BLOCKQUOTE
></DIV
></DD
><DT
><A
NAME="LIBPQ-PQESCAPESTRINGCONN"
></A
><CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
>
      </DT
><DD
><P
></P><PRE
CLASS="SYNOPSIS"
>size_t PQescapeStringConn(PGconn *conn,
                          char *to, const char *from, size_t length,
                          int *error);</PRE
><P>
     </P
><P
>      <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
> escapes string literals, much like
      <CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
>.  Unlike <CODE
CLASS="FUNCTION"
>PQescapeLiteral</CODE
>,
      the caller is responsible for providing an appropriately sized buffer.
      Furthermore, <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
> does not generate the
      single quotes that must surround <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> string
      literals; they should be provided in the SQL command that the
      result is inserted into.  The parameter <TT
CLASS="PARAMETER"
>from</TT
> points to
      the first character of the string that is to be escaped, and the
      <TT
CLASS="PARAMETER"
>length</TT
> parameter gives the number of bytes in this
      string.  A terminating zero byte is not required, and should not be
      counted in <TT
CLASS="PARAMETER"
>length</TT
>.  (If a terminating zero byte is found
      before <TT
CLASS="PARAMETER"
>length</TT
> bytes are processed,
      <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
> stops at the zero; the behavior is
      thus rather like <CODE
CLASS="FUNCTION"
>strncpy</CODE
>.) <TT
CLASS="PARAMETER"
>to</TT
> shall point
      to a buffer that is able to hold at least one more byte than twice
      the value of <TT
CLASS="PARAMETER"
>length</TT
>, otherwise the behavior is undefined.
      Behavior is likewise undefined if the <TT
CLASS="PARAMETER"
>to</TT
> and
      <TT
CLASS="PARAMETER"
>from</TT
> strings overlap.
     </P
><P
>      If the <TT
CLASS="PARAMETER"
>error</TT
> parameter is not <TT
CLASS="SYMBOL"
>NULL</TT
>, then
      <TT
CLASS="LITERAL"
>*error</TT
> is set to zero on success, nonzero on error.
      Presently the only possible error conditions involve invalid multibyte
      encoding in the source string.  The output string is still generated
      on error, but it can be expected that the server will reject it as
      malformed.  On error, a suitable message is stored in the
      <TT
CLASS="PARAMETER"
>conn</TT
> object, whether or not <TT
CLASS="PARAMETER"
>error</TT
> is <TT
CLASS="SYMBOL"
>NULL</TT
>.
     </P
><P
>      <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
> returns the number of bytes written
      to <TT
CLASS="PARAMETER"
>to</TT
>, not including the terminating zero byte.
     </P
></DD
><DT
><A
NAME="LIBPQ-PQESCAPESTRING"
></A
><CODE
CLASS="FUNCTION"
>PQescapeString</CODE
>
      </DT
><DD
><P
>       <CODE
CLASS="FUNCTION"
>PQescapeString</CODE
> is an older, deprecated version of
       <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
>.
</P><PRE
CLASS="SYNOPSIS"
>size_t PQescapeString (char *to, const char *from, size_t length);</PRE
><P>
     </P
><P
>      The only difference from <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
> is that
      <CODE
CLASS="FUNCTION"
>PQescapeString</CODE
> does not take <TT
CLASS="STRUCTNAME"
>PGconn</TT
>
      or <TT
CLASS="PARAMETER"
>error</TT
> parameters.
      Because of this, it cannot adjust its behavior depending on the
      connection properties (such as character encoding) and therefore
      <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>it might give the wrong results</I
></SPAN
>.  Also, it has no way
      to report error conditions.
     </P
><P
>      <CODE
CLASS="FUNCTION"
>PQescapeString</CODE
> can be used safely in
      client programs that work with only one <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
      connection at a time (in this case it can find out what it needs to
      know <SPAN
CLASS="QUOTE"
>"behind the scenes"</SPAN
>).  In other contexts it is a security
      hazard and should be avoided in favor of
      <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
>.
     </P
></DD
><DT
><A
NAME="LIBPQ-PQESCAPEBYTEACONN"
></A
><CODE
CLASS="FUNCTION"
>PQescapeByteaConn</CODE
>
      </DT
><DD
><P
>       Escapes binary data for use within an SQL command with the type
       <TT
CLASS="TYPE"
>bytea</TT
>.  As with <CODE
CLASS="FUNCTION"
>PQescapeStringConn</CODE
>,
       this is only used when inserting data directly into an SQL command string.
</P><PRE
CLASS="SYNOPSIS"
>unsigned char *PQescapeByteaConn(PGconn *conn,
                                 const unsigned char *from,
                                 size_t from_length,
                                 size_t *to_length);</PRE
><P>
      </P
><P
>       Certain byte values must be escaped when used as part of a
       <TT
CLASS="TYPE"
>bytea</TT
> literal in an <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> statement.
       <CODE
CLASS="FUNCTION"
>PQescapeByteaConn</CODE
> escapes bytes using
       either hex encoding or backslash escaping.  See <A
HREF="datatype-binary.html"
>Section 8.4</A
> for more information.
      </P
><P
>       The <TT
CLASS="PARAMETER"
>from</TT
> parameter points to the first
       byte of the string that is to be escaped, and the
       <TT
CLASS="PARAMETER"
>from_length</TT
> parameter gives the number of
       bytes in this binary string.  (A terminating zero byte is
       neither necessary nor counted.)  The <TT
CLASS="PARAMETER"
>to_length</TT
>
       parameter points to a variable that will hold the resultant
       escaped string length. This result string length includes the terminating
       zero byte of the result.
      </P
><P
>       <CODE
CLASS="FUNCTION"
>PQescapeByteaConn</CODE
> returns an escaped version of the
       <TT
CLASS="PARAMETER"
>from</TT
> parameter binary string in memory
       allocated with <CODE
CLASS="FUNCTION"
>malloc()</CODE
>.  This memory should be freed using
       <CODE
CLASS="FUNCTION"
>PQfreemem()</CODE
> when the result is no longer needed.  The
       return string has all special characters replaced so that they can
       be properly processed by the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
       string literal parser, and the <TT
CLASS="TYPE"
>bytea</TT
> input function. A
       terminating zero byte is also added.  The single quotes that must
       surround <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> string literals are
       not part of the result string.
      </P
><P
>       On error, a null pointer is returned, and a suitable error message
       is stored in the <TT
CLASS="PARAMETER"
>conn</TT
> object.  Currently, the only
       possible error is insufficient memory for the result string.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQESCAPEBYTEA"
></A
><CODE
CLASS="FUNCTION"
>PQescapeBytea</CODE
>
      </DT
><DD
><P
>       <CODE
CLASS="FUNCTION"
>PQescapeBytea</CODE
> is an older, deprecated version of
       <CODE
CLASS="FUNCTION"
>PQescapeByteaConn</CODE
>.
</P><PRE
CLASS="SYNOPSIS"
>unsigned char *PQescapeBytea(const unsigned char *from,
                             size_t from_length,
                             size_t *to_length);</PRE
><P>
      </P
><P
>       The only difference from <CODE
CLASS="FUNCTION"
>PQescapeByteaConn</CODE
> is that
       <CODE
CLASS="FUNCTION"
>PQescapeBytea</CODE
> does not take a <TT
CLASS="STRUCTNAME"
>PGconn</TT
>
       parameter.  Because of this, <CODE
CLASS="FUNCTION"
>PQescapeBytea</CODE
> can
       only be used safely in client programs that use a single
       <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> connection at a time (in this case
       it can find out what it needs to know <SPAN
CLASS="QUOTE"
>"behind the
       scenes"</SPAN
>).  It <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>might give the wrong results</I
></SPAN
> if
       used in programs that use multiple database connections (use
       <CODE
CLASS="FUNCTION"
>PQescapeByteaConn</CODE
> in such cases).
      </P
></DD
><DT
><A
NAME="LIBPQ-PQUNESCAPEBYTEA"
></A
><CODE
CLASS="FUNCTION"
>PQunescapeBytea</CODE
>
      </DT
><DD
><P
>       Converts a string representation of binary data into binary data
       &mdash; the reverse of <CODE
CLASS="FUNCTION"
>PQescapeBytea</CODE
>.  This
       is needed when retrieving <TT
CLASS="TYPE"
>bytea</TT
> data in text format,
       but not when retrieving it in binary format.

</P><PRE
CLASS="SYNOPSIS"
>unsigned char *PQunescapeBytea(const unsigned char *from, size_t *to_length);</PRE
><P>
      </P
><P
>       The <TT
CLASS="PARAMETER"
>from</TT
> parameter points to a string
       such as might be returned by <CODE
CLASS="FUNCTION"
>PQgetvalue</CODE
> when applied
       to a <TT
CLASS="TYPE"
>bytea</TT
> column. <CODE
CLASS="FUNCTION"
>PQunescapeBytea</CODE
>
       converts this string representation into its binary representation.
       It returns a pointer to a buffer allocated with
       <CODE
CLASS="FUNCTION"
>malloc()</CODE
>, or <TT
CLASS="SYMBOL"
>NULL</TT
> on error, and puts the size of
       the buffer in <TT
CLASS="PARAMETER"
>to_length</TT
>. The result must be
       freed using <CODE
CLASS="FUNCTION"
>PQfreemem</CODE
> when it is no longer needed.
      </P
><P
>       This conversion is not exactly the inverse of
       <CODE
CLASS="FUNCTION"
>PQescapeBytea</CODE
>, because the string is not expected
       to be <SPAN
CLASS="QUOTE"
>"escaped"</SPAN
> when received from <CODE
CLASS="FUNCTION"
>PQgetvalue</CODE
>.
       In particular this means there is no need for string quoting considerations,
       and so no need for a <TT
CLASS="STRUCTNAME"
>PGconn</TT
> parameter.
      </P
></DD
></DL
></DIV
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